James Holmes, the former PhD-student accused of killing 12 people in Colorado when he opened fire in a cinema during a midnight screening of Batman, intends to plead not guilty by reason of insanity, his lawyers have said.

Dzhokhar Tsarnaev, the 19-year-old charged with setting off the shrapnel-packed pressure cooker bombs that killed three people at last week's Boston Marathon has been transferred from a civilian hospital to a federal medical detention centre.

The nation’s dwindling band of smokers, skulking outside office doors, already resent being treated as pariahs. The suggestion that they may be dotty, too, will only enrage them further. But the argument is not as daft as it seems. It is a matter of statistics.